Chapter 7

Thermal and Other Methods of Material Removal

Hot Wire Cutting

  • Used to cut foamed thermoplastic material (Thermoplastic - Soften repeatedly when heated)
  • Requires good ventilation
  • Cannot cut thermosetting polymers, insulation materials or polyurethane foam (Thermosetting -When hardened cannot melt again)

Oxy-Fuel Gas Cutting

A cutting torch uses a circle of oxy-fuel jets to bring the material to its melting point then compressed oxygen is released in a center nozzle to “blow away” the molten metal.

  • Typical oxy-fuel is oxygen-acetylene or oxygen-hydrogen
  • It is a fast, inexpensive process that requires fairly little operator training.
  • Plates as thick as 12 inches may be cut
  • Industry often uses computer controlled machines with multiple cutting torches to produce multiple parts simultaneously.

LASER Cutting - source of energy is a light -Light Amplification by Stimulated Emission of Radiation

  • Uses a highly focused light source as energy
  • Removes metal by melting and then vaporizing the workpiece, gas blows liquid and vapor away
  • Reflectivity and thermal conductivity of materials are important (dull materials preferred)
  • A gas stream helps to clear the path for beam
  • Small holes with deep depth can be made the size of the laser beam (blind holes cannot be made to exact depth)
  • Never look into a laser – can cause major damage to retina

i)Advantages

(1)Material savings from very narrow kerf

(2)Minimum heat effected zone

(3)Fine finishes on thin pieces

(4)Cut complicated shapes

(5)Can cut material of any hardness

(6)Can produce short runs quickly and efficiently

ii)Disadvantages

(1)Cost of machine can be as high as $2 million and more

(2)Cost of maintenance can be $4,000 per machine per month

Water Saw (Waterjet)

Water that has been filtered for minerals and debris is increased in pressure from 20,000 to 60,000 psi and forced through a small orifice (0.003” to 0.023”) to cut through material

Plastics, fabrics, rubber, wood products, paper, leather, insulating materials, brick, composite materials

Examples:

Vinyl and foam coverings for automobile dashboards, automotive carpet patterns, concrete removal, food processing, paper industry

Electron Beam Machining - high velocity electrons strike work piece causing heat and melt the work piece

a)Voltages of 50,000-200,000 V

b)Must be done in a vacuum or loss of power results

c)Makes cuts accurately on smaller size work pieces

Advantages / Disadvantages
Oxy-Acetylene Flame / Fast; can be used on large cuts / Rougher cut surface
Workpiece surface oxidized
Electron Beam / clean; good precision / Expensive; requires vacuum
Water Saw / Good on hard materials
Relatively fast / . Expensive equipment